(1) Field of the Invention
The present invention relates to novel carboxyalkyl acetyl celluloses having a high degree of substitution by the carboxyalkyl group and acetyl group per anhydroglucose unit (hereinafter each "degree of substitution" means that per anhydroglucose unit), their salts and a process for the preparation of them.
(2) Description of the Prior Art
There are a few reports on carboxyalkyl acetyl celluloses. As to carboxyalkyl acetyl celluloses whose carboxyalkyl groups are of acid-form, their use as an enteric coating agent, relying on their solubility in organic solvents and their solubility in intestines, is described (Japanese Patent Publication No. 35393/1971. It is disclosed that said carboxalkyl acetyl celluloses have a degree of substitution by the carboxyalkyl group of 0.3-1.2. However, there is given no disclosure as to the degree of substitution by acetyl group of such carboxyalkyl acetyl celluloses and the process for the preparation of them. Further, a process for the acetylation of carboxymethyl cellulose (British Pat. No. 1,126,244) and an instance of acetylation using a large amount of acetic anhydride in the presence of catalyst, after an alkali cellulose is reacted with monochloroacetic acid, (U.S.S.R. Inventor's Certificate Specification No. 612933) are known. These acetylation processes, however, have such defects that the acetyl groups eliminated in the course of the reaction or a large amount of acetic anhydride is required. Carboxyalkyl acetyl celluloses obtained by the former process are very low in their degree of substitution by the carboxyalkyl group, and those obtained by the latter process are very low in their degree of substitution by acetyl group. Carboxyalkyl acetyl celluloses having a high degree of substitution by both carboxyalkyl group and acetyl group are not known as yet.